Power regulator



Awa-15, 1941.

.1. N. wHiTAKER POWER REGULATOR Filed oct. 5i, 1939 INVEN TOR.

Wf//TAKER ATTORNEY.

Patented Apr. 15, 1941 i y2,238,262 y POWER nEGULA'roR James N. Whitaker, Weehawken, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 31, 1939, Serial No. 302,109

12 Claims.

This invention relates to power regulators and more particularly to a device which is enabled to provide either variable power regulation or constant power regulation, depending upon the usev to which the device is to be put.`

Gaseous discharge tubes of the triggerdacting type have been used in various ways for power control in alternating current systems. Such systems are used, for example, for controlling illumination in theaters and in similar applications. The method generallyv adopted is one which employs so-called thyratron tubes, where a greater 4or lesser value of negative bias on the grid of the tube causes the conduction of electrical energy to start at a point nearer .to or farther from the positive peak of each cycle.

It is an object of the present invention to provide a system of power regulation suitable forany one'of a variety of different uses, depending upon the load conditions which are to be served.

It is another object of my invention to provide a suitable current regulator for use in connection with a photographic iilm printer whereby the density of .the negative film is caused to control a current supply system for the energization of a printing light source.

It is another object of myy invention to provide a variable power supply dependent upon the action of a photo-electric device, such as used in facsimile picture transmission systems, for producing a variable amplitude picture signal.

Other objects alpin to those already recited are contemplated and will be apparent upon reviewing the description to` follow. The invention itself will best be understood by reference ,g to the accompanying drawing, in whichcomprising a cathode 3, an anode 4, a control grid 5 and, if desired, a suppressorgrid 6. Within the envelope of the tube is a low pressure gaseous atmosphere. Such tubes are commonly termed thyratron tubes. Other types of gaseous tubes, however, may be used in my invention without departing from the spirit thereof.

The -anodes 4 of the tubes I and 2 are connected respectively to different secondary winding terminals 24 and 25 of a transformer l. The prim-ary of this transformer is fed with energy from any suitable alternating current source. The secondary of the transformer I has a midtap 8 which is connected to a mid-tap 9 on the primary winding of a transformer I0. The terminals of the primary winding on transformer I0 are connected respectively to the two cathodes 3 and to the suppressor grids 5 of the tubes I and 2. Interposed between-each cathode 3 and its associated control grid 5 is a bias resistor II. Each control grid 5 is also connected to an appropriate anode I2 in a photo-electric .tube I3. The two photo-electric tubes are preferably housed in a container Il having an opening I5 disposed in back of a lm gate. This gate has a front plate I8 with van opening Il therein which serves to admit light from a lamp I8 for print-l ing purposes. Any suitable arrangement of lm guides may -be provided such as rollers I9 for the negative `film and rollers 20 for the film to be printed.

Each of the photo-electric tubes I3 possesses a cathode 2|. having a proper connection to one of the terminals 24 and 25 on the secondary of the transformer I. The energizing circuit for the lamp I8 comprises the secondary winding 22 on the transformer I0 and a rheostat 23 for adjusting the normal light intensity with respect to the speed at which the films are to be moved for printing purposes.

The system as exemplified n Fig. 1 is intended to function so as to vary the light intensity of the printing lamp I8 in dependence upon variations of negative film density occurring at or near the position of printing exposure. Some of the light from the lamp I8. penetrates both the negative film andthe film to be printed. This light acts upon the photo-electric cathodes I3 to vary .the electronic emission therefrom. If desired, the photo-electric tubes can be placed in advance of the printing exposure window I'I so .as to receive light through the negative film only.

. on its anode 4. The ionizing voltage is varied in dependence upon the bias applied to the control grid 5,.

Let it be assumed that the potential at the terminal 24 is rising on a positive half cycle of current. Let it be assumed also that the portion of the negative lm in back of the window l1 is so dense that very little light penetrates the two films so as to reach the photo-electric cathodes 2l of tubes I3. Under these conditions substantially no current flows through the bias resistors M and consequently the grids 5 are held at substantially cathode potential. vThe thyratron tube Il almost immediately becomes conductive. The thyratron tube 2 acts in the same manner upon reversal ofl current across the transformer terminals 2d and 25. Considering the action of tube I, however,'current is passed from the terminal 2d of the transformer 'l through the space discharge path of the -tube l to the cathode 3 and thence to the left-hand terminal of the primary winding on the transformer jl@ and back through the center tap S to Ithe center tap 8 of the transformer 77. Asthis action continues energy will be supplied to the lamp It. The duration of the conductive state will be greater in thls case than in the case now to be described.

Assume now that a more translucent portion of the negative is to be printed and vis in back of 'the window V1. Under these conditions photo-electric action will take place in the tubes I3. Considering onlyA the left-hand tube I3, however,

` a negative potential derived from the terminal 25 of the secondary on transformer l Will produce a conductive state in the tube I3, which is intensified by the light impressed on the cathode 2|, and this operation will draw current through the bias resistor II, thereby rendering the control grid 5 more negative than the cathode 3. It follows that a period of cut-off bias on the tube I will be prolonged, and the duration of the conductive state when the anode potential eventually reaches the ignition point will be shortcned. The reduced time of conductivity of the tube results in the application of less power to the transformer I0, and accordingly the lamp I8 will be somewhat dimmed to compensate for the more translucent area of the negative.

Referring to Fig. 2, I show diagrammatically how the wave form of an alternating current may be modified by the control process above described. Here the outline of a sine wave can vbe observed over a certain portion thereof, but

this outline is broken by certain periodsv of nonconductance of the thyratron tubes. The duration of the conductive state in tube I is shown between the two vertical dimension lines at the extremities of a positive peak. Theduration of the conductive state in tube 2 is correspondingly indicated by dimension lines at the extremities of a subsequent peak which is positively impressed on the anode of tube 2, although it represents a half cycle of opposite phase. It will be understood that by varying the instant of ionization of the gas in each thyratron tube under control of the grid bias potentials derived from the photo-electric tubes I3, these moments of duration of the conductive state may be correspondingly varied.

It will be clear from the above description that I have provided a combination of gaseous tubes and photo-electric tubes which cooperate for varying the intensity of a light source in dependence upon the density of a negative lm from which a printing operation is to be performed on an unexposed film. The variation in the conductive time interval of the gaseous tube during each positive half cycle applied to its -across the bias resistors II.

anode circuit corresponds with a variation in the R. M. S. voltage of the output energy. Hence the device operates as an output power modulator. Various modifications in the structural parts of the film printer may be made, of course, without departing from the spirit of the invention.

Referring now to Fig. 3, I show another application of my invention as it may be used in connection with a facsimile transmitter. Parts corresponding to those in Fig. 1 have been given like reference numbers.

In the embodiment shown in Fig. 3 a different set of conditions is met compared with those set forth in connection with the embodiment of Fig. 1. For facsimile picture signal transmission it is essential that a constant light source 23 lbe employed. The lamp 23 may be excited from any suitable direct current source 2l. The

intensity of the light may be controlled by a rheostat 23.

A suitable optical system consisting of lenses 29 may be employed to focus a light spot upon an elemental area of a picture to be scanned for facsimile signal transmission requirements. A scanning drum is shown at 30 and will be understood to have wrapped around it a. picture which is to be used for picture signal transmission. As the drum is rotated at a constant speed it is also moved axially with respect to the light spot so as to form a helical scanning path which eventually covers the entire picture.

The light at the scanning spot is reflected from the surface of the picture in greater or lesser intensity, according to the light and dark elemental areas of the picture. The reflected light shines upon an optical system which may, if desired, comprise lenses 3l and a prism 32, so as to be impressed upon the photo-electric cathodes 2i of the two .photo-electric tubes I3.

The operation of the gaseous tubes I and 2 as shown in Fig. 3 will be readily understood from the description which has been given of these tubes in Fig. 1.` However, the output energy which results from controlling the duration of the conductive state in each of the tubes I and 2 is impressed upon the primary winding of a transformer 33. This transformer has a secondary winding 32 which delivers a picture signal, preferably for radio or wire transmission purposes.

In the operation of the systemshown in Fig. 3 it will be understood that a relatively dark elemental area, when it comes beneath the light spot projected from the lamp 26, will produce very little light reflection through the optical system of lenses 3| and prism 32 to the cathodes 2I of the photo-electric tubes I3. Consequently these photo-electric tubes will be substantially non-conductive and there will be little, if any.

negative bias on the thyratron control grids 5,

since no current will pass through the bias rey sistors II.

Under the condition, however, where the elemental picture area that is scanned is relatively white, then considerable light will be reected into the optical system 3l, 32 and will reach the photo-electric cathodes 2l so as to render these tubes sufficiently conductive to draw current 'I'he grids 5 in the gaseous tubes will then be rendered more negative and the duration of the conductive state in each of the tubes I and 2 will be shortened. Under these conditions a reduced amplitude of signal will be impressed upon the output circuit from the secondary winding 34 oi the transformer 33. It will be seen from this description that the system as shown is one wherein maximum amplitude of the picture signal represents a black area and minimum amplitude represents a white area. This relationship between the amplitude and light intensity may, however, be reversed by refversing the action of the photo-electric tubes I3 so as to render the grids of the thyratron tubes more positive with increase in light intensity.

My invention has still another group of applications which may well be understood by considering Fig. 1 without the inclusion of the films. Assume, for example, that it isrmerely required that the device be used as a voltage regulator.

The secondary winding 22 of the transformer I0 may then be used to deliver energy to anyv required load. In parallel with this load is the circuit for exciting the lamp I8. Without the negatives in the light path between the lamp I8 and the photo-electric tubes I3, it will be seen that variations in the load or variations in the input voltage on the transformer 'I may be compensated. 'I'he compensating action results from variations in the light intensity of the lamp I8 due to a fluctuating load or to a iiuctuating input voltage. However, this light fluctuation from the lamp I8 operates upon the photo-electric tubes I3 so as to vary the bias across the resistors II, and thus to vary the duration of the conductive state in each of the tubes I and 2. The portion of each cycle of the alternating current which is lost will be subtracted from the total power available at the terminals 2l and 25 of the transformer. Regulation of the R. M S. voltage thus results. Assuming that, for a given period, the load is substantially constant, -an equilibrium will be reached when the power passed by the Thyratron tubes is just suicient to produce a constant value of illumination from the lamp I8. Ii, after this equilibrium is established, the load increases so as to reduce the output voltage across the secondary winding 22, then the brilliance of the lamp I8 will be reduced, the conductance of the photo-electric tubes I3 will be reduced, and the negative bias on grids 5 of the Thyratron tubes will be reduced so as to lengthen the conductive state in the tubes I and 2. Thus, R. M. S. voltage compensation will be provided to meet the added load.

Various other applications of my invention will suggest themselves to those skilled in the art upon considering the exemplified applications herein shown and described. The invention is, therefore, limited only in accordance with the scope of the claims.

I claim:

l A power control system for use between an alternating powery supply source and a load, said system comprising at least one trigger-acting gaseous discharge tube having its discharge path determined by a cathode and an anode, said discharge path being in circuit between said source and said load, a control grid in said discharge path, a bias resistor interconnecting the control grid and the cathode. a photo-electric device having one electrode connected to said source and a second electrode directly connected to the control grid of said gaseous tube, and means including a light source acting upon said photo-electric device for varying the electronic discharge therein, thereby to control the bias on said control. grid, said means being solely effective to vary the interval of the conductive state of said gaseous tube during a half cycle of current from said source.

2. A system in accordance with claim 1 and having means for varying the intensity of said light source in dependence upon the R. M. S. voltage applied to said load. I

3. A system in accordance with claim 1 and having amedium of variable translucence interposed between said light source and said photoelectric device.

4. A system in accordance with `claim 1 and having a medium suitably disposed for reflecting light from said light source toward said photoelectric device, said medium having light and dark areas and being movable to vary the amount of light which it reiiects.

5. A current regulator for use between an alternating power supply source and a load, said regulator comprising at least one trigger-acting gaseous discharge tube having a control grid in theA discharge path thereof, said discharge path being in circuit between said source and said load, a lamp in the load circuit, and a photo-electric device' arranged to receive iight'from said lamp, said device having connections between said power source and the control grid of said gaseous tube such that the duration of the conductive state of said gaseous tube within a half cycle of current from said source is controlled in dependence upon the amount of light reaching the photo-electric device from said lamp.

6. A voltage regulator comprising an input transformer, a pair of gas discharge tubes each having an anode, a cathode and a control grid, the two said anodes being connected respectively to opposed' secondary terminals of said transformer., an output transformer having opposed primary terminals connected respectively to each said cathode, interconnected mid-taps on the secondary of said input transformer and on the primary of said output'transformer, a load connected across the secondary of said output transformer, said load including a light source, bias resistors, each connected between the cathode and control grid of a respective discharge tube, and two photo-electric devices each having a discharge path in circuit between the control grid of one gas tube and the anode of the other gas tube respectively. said devices being arranged for photo-electric response to variations in the light impinging thereon from said light source.

7. A voltage `regulator in accordance with claim 6 and having a variably translucent medium interposed in the light pathbetween said light source and said photo-electric devices whereby the R. M. S. voltage applied to said light source is caused to be varied in dependence upon the translucence of said medium. 1

8. In a device of the class described, an input transformer, a pair of gas discharge tubes each having an anode, a cathode and a control grid, the two said anodes being connected respectively to opposed secondary terminals of said transformer, an output transformer having opposed primary terminals connected respectively to each said cathode, interconnected mid-taps on the secondary of said input transformer and on the primary of said output transformer, alight source connected across the secondary of said output transformer, bias resistors connected respectively between the cathode and control grid of each tube, two photo-electric devices each having a discharge path in circuit between the control grid of one gas tube and the anode of the other gas tube respectively, and means interposed in the light path from said light source to said photoelectric devices for varying the photo-response in said devices thereby to control the grids of said gas discharge tubes and to vary the R. M. S. voltage derived therefrom.

9. A circuit arrangement comprising a pair of gaseous discharge tubes each having a cathode, an anode and a control grid, two bias resistors each respectively interconnecting the control grid and the cathode of the same tube, two photoresponsive impedances each respectively in circuit between the control grid of one tube and the anode of the other tube, an alternating current input circuit having push-pull connections to said anodes and oppositely phased connections to said cathodes, an output transformer having a centertapped primary Winding the respective halves of which are separately connected to said cathodes, the center-tap of said primary winding being connected to a neutral point on said input circuit, and means for controlling the bias on said grids by causing light of varying intensity to shine on said photo-responsive irnpedances..

bias controlling means comprises a light source connected across the terminals of said output transformer, said light source being arranged to act upon said photo-responsive impedances. V

l1. A powericompensating device comprising the circuit arrangement according to claim 9, wherein the bias controlling means comprises a light source connected across the terminals of said output transformer., and' a variably translucent medium through which light rays from said light source impinge upon said photo-responsive impedances..

12. A modulator comprising the circuit arrangement according to claim 9, wherein the bias controlling means comprises a constant light source, a movable reflecting medium having light and dark areas thereon, means for focussing a beam of light from said 'light source on said refleeting medium, and means for causing varying amounts of light reected from said medium to impinge upon said photo-responsive impedances.

JAMES N. WEHTAKER. 

